(1) Field of the Invention
The present invention relates to semiconductor devices and methods for fabricating the same, and more particularly relates to the structures of silicide layers and formation methods for the same.
(2) Description of Related Art
In general metal oxide semiconductor (MOS) transistors, reduction of parasitic resistance such as contact resistance and wiring resistance is important in increasing operation speed. The reduction of parasitic resistance in such transistors is generally achieved by siliciding upper portions of source/drain regions and upper portions of gate electrodes.
To increase the integration degree of a large-scale semiconductor integrated (LSI) circuit device, reduction of the vertical size as well as the horizontal size is needed. A method in which the junction depth of a doped layer to be source/drain regions is reduced is used as one of methods for reducing the vertical size,. However, if the thickness of the doped layer in the semiconductor substrate is small, there arises a problem in which the resistance of the doped layer increases so that the operation speed of the semiconductor device decreases. To prevent this decrease, it is effective to reduce the source/drain resistance by using a structure in which a metal silicide layer is formed in the surface of the doped layer. The following method has conventionally been used as a method for forming metal silicide layers: A metal film is deposited to cover a silicon substrate and polysilicon that will be a gate electrode and subjected to heat treatment so that metal and silicon react with each other to form silicide in upper portions of source/drain regions and an upper portion of the gate electrode. In a case where impurity diffusion layers forming source/drain regions are allowed to have a shallow junction structure, a material capable of reducing the amount of silicon consumed during silicidation needs to be used as a material for silicide layers.
A silicide formation technique using, as a material capable of reducing the amount of silicon consumed, nickel (Ni) that forms low-resistance monosilicide has been developed.
However, it has been known that NiSi2, which is a disilicide phase of Ni silicide, has a lattice constant fairly close to that of silicon and forms an inverted-pyramidal interface by subsequent high-temperature heat treatment or under inappropriate process conditions. A method for forming an alloyed silicide has been proposed as a method for forming Ni silicide with stability by enhancing resistance (heat resistance) to subsequent high-temperature heat treatment (see, for example, patent literature 1: U.S. Pat. No. 6,689,688). In this patent, examples of elements providing the effect of stabilizing NiSi, which is a low-resistance monosilicide phase, by being added to NiSi include Ge, Ti, Re, Ta, N, V, Ir, Cr and Zr (see, for example, non-patent literature 1: Min-Joo Kim, Hyo-Jick Choi, Dae-Hong Ko, Ja-Hum Ku, Siyoung Choi, Kazuyuki Fujihara, and Cheol-Woong Yang, “High Thermal Stability of Ni Monosilicide from Ni—Ta Alloy Films on Si(100)”, Electrochem. Solid-State Lett. 6, 2003, G122). In addition, it is suggested in a report that Hf, which is an element exhibiting physical/chemical properties similar to those of Zr, also has a similar effect (see, for example, non-patent literature 2: R. Xiang (in Tokyo institute of Technology) et al., “Formation of Ni Silicide by Addition of Hf”, Preliminary Material for 65th Annual Meeting of Japanese Society of Applied Physics, P. 708, Sep. 1 to 4, Autumn in 2004 (Lecture No. 2P-M-10)). It is also suggested in other reports that elements such as Mo, Ir, Co and Pt have similar advantages (see, for example, non-patent literature 3: Young-Woo Ok, Chel-Jong Choi, and Tae-Yeon Seong, “Effect of a Mo Interlayer on the Electrical and Structural Properties of Nickel Silicides”, J. Electrochem. Soc. 150, 2003, G385, non-patent literature 4: Jer-shen Maa, Yoshi Ono, Douglas J. Tweet, Fengyan Zhang, and Sheng Teng Hsu, “Effect of interlayer on thermal stability of nickel silicide”, J. Vac. Sci. Technol. A 19, 2001, pp. 1595, and non-patent literature 5: D. Mangelinck, J. Y. Dai, J. S. Pan, and S. K. Lahiri, “Enhancement of thermal stability of NiSi films on (100)Si and (111)Si by Pt addition”, Appl. Phys. Lett., 1999, vol.75, num.12, pp. 1736).